In the production of cigarette filters, which have at least two portions of different material consistency when viewed along their longitudinal extent, there is a difficulty that the filter rods cut off from the continuously produced cigarette filter strand must not only have a constant length but also that the cuts must also be made always at the same place of a specific filter portion so that identical filter rods of the same defined composition can be obtained.
The prior art already discloses a method for controlling the cutting device of a cigarette filter production machine in which the filter strand is capacitatively tested by means of a high-frequency electric field. However, at high filter strand speeds of up to 2 m/s and more this method produces insufficiently sharply defined measuring signals, a feature which makes very precise control of the cutting speed impossible at high filter strand speeds.